Ventilation vents in automobiles have air direction deflectors or louver blades on a rotor which are rotatable about a vertical or horizontal axis for discharge of air at selected angles. The individual baffles can also be adjusted to deflect the air at a certain angle relative to the horizontal axis. As a result of wear of the bearings and vibrations due to travel, the rotors shift from the selected position. There is no positive stop provided to fix the ventilation rotors at the selected angle and prevent displacement.